Polymers containing silver and copper derived from cyano and sulfonic containing monomers

ABSTRACT

NEW POLYMERS AND COPOLYMERS CONTAINING SILVER AND/OR COPPER, USEFUL E.G. IN MANUFACTURING DIALYSE AND FILTRATION MEMBRANES, ION EXCHANGERS, LIGHT SENSITIVE LAYERS, CATALYSTS AND HYDROPHILIC COATINGS, ARE PREPARED FROM COPOLYMERS OR POLYMER MIXTURES CONTAINING BOTH NITRILE GROUPS AND STRONG ACIDIC GROUPS, BY RINGING THEM IN CONTACT WITH MONOVALENT SILVER OR COPPER IONS OR WITH THEIR MIXTURES. SILVER AND/OR COPPER ARE ATTACHED TO NITRILE GROUPS BY SIDE VALANCES, FORMING THUS COMPLEX COMPOUNDS. THE PROBABLE FORMULAE OF THE COMPLEX SIDEGROUPS ARE: -CN.AG+ OR PERHAPS -CN.AG+.NC- AND -CN.CU+ OR PERHAPS -CN.CU+.CU+.NC-, THE COMPLEX CATIONS FORMING POLYMERIC SALTS WIT STRONG ACIDIC GROUPS OF THE SAME OF AN ADJOINING MACROMOLECULE, TO WHICH ALL SAID NITRILE AND STRONGLY ACIDIC GROUPS ARE ATTACHED AS THEIR SIDE SUBSTITUENTS.

United States Patent 3,734,897 POLYMERS CONTAINING SILVER AND COPPERDERIVED FROM CYANO AND SULFONIC CON- TAINING MONOMERS Arthur Stoy,Prague, Czechoslovakia, assignor to Ceskoslovenska Akademie ved, Prague,Czechoslovakia No Drawing. Continuation of abandoned application Ser.No. 729,897, May 17, 1968. This application Feb. 9, 1971, Ser. No.114,088

Int. Cl. C08f 13/00; C12g 1/00; G03c N86 US. Cl. 260-795 MU 8 ClaimsABSTRACT OF THE DISCLOSURE New polymers and copolymers containing silverand/ or copper, useful e.g. in manufacturing dialyse and filtrationmembranes, ion exchangers, light sensitive layers, catalysts andhydrophilic coatings, are prepared from copolymers or polymer mixturescontaining both nitrile groups and strong acidic groups, by bringingthem in contact with monovalent silver or copper ions or with theirmixtures. Silver and/or copper are attached to nitrile groups by sidevalences, forming thus complex compounds. The probable formulae of thecomplex sidegroups are: CN.Ag+ or perhaps CN.Ag+.NC and CN.Cu or perhapsCN.Cu+.Ou+.NC-, the complex cations forming polymeric salts with strongacidic groups of the same or of an adjoining macromolecule, to which allsaid nitrile and strongly acidic groups are attached as their sidesubstituents.

This application is a continuation of Ser. No. 729,897 filed May 17,1968, now abandoned.

Polymers and copolymers forming starting materials for the new complexpolymeric compounds, are mainly derived from acrylonitrile ormethacrylonitrile on the one hand and from ethylene sulfonic or styrenesulfonic acid on the other, said monomers forming either copolymers ormixtures of homopolymers.

Copolymers of this kind were known. It was not known, however, that theycan form complex compounds with silver and monovalent copper having newand in many respects outstanding properties. There were known onlychelates of silver and copper ions with polymers having iminodiaceticgroups (so called IDE-resins, see e.g. R. Hering, ChelatbildendeIonenaustauscher, Akademie-Verlag Berlin 1967, p. 91-93).

There was also known a method of dyeing polyacrylonitrile fibres withacid dyestuffs in presence of monovalent copper salts-sandocryl andother processes. In said processes, the strongly acidic groups wereattached to dyestulf molecules only, not to macromolecules of the sameor other polymer. Complex-bound dyestutf molecules were concentratedmainly near the surface of the fibre and the properties of the fibreremained unchanged except the color. Although the said dyeing method wasknown for many years, there was no hint in the art how to use theafiinity of cuprous ions to nitrile groups for other purposes thandyeing. The possibility of using silver ions for modifying polymershaving nitrile groups was apparently not studied at all.

Although any polymer or copolymer having nitrile side groups may be usedfor the purpose of the invention, e.g. methacrylonitrile orvinylidencyanide polymers, acrylonitrile polymers and copolymers arepreferred since they are more accessible, less expensive and more strongand stable than others. From strongly acidic groups the sulfonic groupsare preferred from similar reasons, although they can be replaced byacid sulfuric ester groups -O.SO H or by phosphoric ester groups such as-O.PO H if desired. Generally, all strongly acidic groups as used in ionexchangers may be employed for the purpose of the invention, butsulfonicacid groups, attached to a carbon atom of either the main chainor a side group, appear to be most useful at the present time.

The reaction between monovalent silver or copper ions and polymericsystems containing nitrile and strongly acidic groups takes placepreferably in aqueous media, but it is generally possible to use anymedium in which said polymeric systems either swell or dissolve, and inwhich said metal cations can exist in suflicient concentrations. Likeother ionic reactions, the forming of the present complex compounds israpid, provided that the polymeric system is either dissolved or highlyswollen so that the difiusion of metal ions is not seriously hindered.

As polymeric systems containing both nitrile and strongly acid groupseither copolymers can be employed, having groups of the two kinds on thesame macromolecule, or also mixtures of polymers, each polymercontaining groups of one kind only, or, at least, groups of one saidkind in prevailing amount. Thus, also mixtures of different copolymerscan be employed. Moreover, the copolymers may contain also other monomerunits such as acrylamide or methacrylamide units, such units securingboth higher solubility and possibility of cross-linking with covalentbonds by means of bifunctional compounds capable of reacting with amidicside-groups.

As mixtures of homopolymers, e.g. a mixture of polyacrylonitrile andpolystyrene sulfonic or polyethylene sulfonic acid or their saltsrespectively in a common solvent such as in concentrated nitric acid canbe used.

If copolymers are formed, particularly for special uses, acrylonitrileon the one side and sodium salt of either ethylene sulfonic acid(vinylsulfonic acid) or styrene sulfonic acid are the preferredmonomers. The copolymerization is to be carried out in solventsdissolving all monomers present. It is also advantageous, in some cases,although not unavoidable to use solvents dissolving not only monomers,but also the copolymer thus formed. Such common solvents for bothmonomers and copolymer are e.g. concentrated aqueous solutions ofcertain salts, particularly zinc chloride, or aqueous dimethylformamide.If the share of the acidic monomer prevails, it is possible to use wateras common solvent. In this way, a rather concentrated aqueous copolymersolution, suitable for further treatment, can be obtained immediately bycopolymerization. Economic advantages of water as both polymerizationmedium and copolymer solvent are obvious. Other advantage is very lowtransfer constant of water, yielding higher average molecular weight.Another advantage of water is the possibility of using redoxpolymerization catalysts or initiators, allowing copolymerization atcomparatively low temperatures, whereby the chain transfer onto themonomers and copolymer is slowed down. Concentrated aqueous zincchloride solutions possess also the two last mentioned advantages, butzinc ions are very difficult to be removed, not mentioning the economy.

Aqueous dimethylformamide or dimethylsulfoxide solutions have thedisadvantage of a comparatively high chain transfer constant, but thiscan be partly avoided by using redox catalysts and low temperatures.Generally, the average molecular weight of copolymers prepared in saidsolvents is comparatively low. Nevertheless, said solvents are veryuseful if the monomer, bearing nitrile groups, prevails.

Ionic bonds between cationic nitrile-silver or nitrilecopper groups andstrong acidic groups particularly the intermolecular ones, cause ioniccross-linking. Moreover, the reaction of nitrile groups with silver orcopper ions and the formation of polymeric inner salts manifests itselfby considerable shrinking of the swollen copolymer.

As a result, the strength of the swollen copolymer increases. Since,however, ionic cross-links can be broken and then restituted withoutnecessity of an activation energy, they do not hinder, incontradistinction to covalent cross-links, molecular orientation bystretching. This circumstance is important since copolymers with manystrongly acidic groups swell considerably in water, whereby theirtenacity is impaired. Thus, they cannot be stretched in swollencondition. In dry condition they are brittle and cannot be stretched aswell except at rather high temperatures. If treated with silver ormonovalent copper ions, such copolymers can be easily stretched in wetcondition, whereby their strength and size stability are enhanced. Itis, however, possible to remove silver or copper ions after thestretching and restitute in this way the starting copolymer in a stateof high molecular orientation, e.g. in the form of a membrane or fibre.Surprisingly, the orientation is at least partly maintained togetherwith improved properties, mainly the size stability at different ionicconcentrations. In other words, the linear swelling and shrinking of thecopolymers is substantially reduced.

Silver containing polymeric compounds according to the invention arelight-sensitive and can be used either directly or after having beenreacted with halogenide ions in photography, picture printing andrelated industries.

New silveror copper containing polymer compounds can be also employedfor special coatings, particularly for ships and other articles immersedpermanently in water. They are smooth and resisting to many undesiredorgamsms.

Polymeric systems (copolymers or polymer mixtures) with both nitrile andstrong acid groups are able to catch silver and/ or cuprous ions evenfrom very diluted solutions, such as from different waste waters. 'Ihus,such waste waters can be utilized for preparing the metal containingpolymers according to the invention, which are simultaneously utilizedfor gaining said metals from waste liquors which are otherwise drained.Silver ions are caught quantitatively.

In the form of membranes, grains or fibres the new silver and/ or coppercontaining polymers can be employed for filtration, as ion exchangers,catalysts, means for artificial aging of spirits, wine and otherbeverages etc.

With prevailing acidic groups the new polymers can be used as cationexchangers. With prevailing nitrile groups, they have properties ofanion exchangers.

Other fields of use are dialysis, electrodialysis, fuel cells and other.

Membranes from the new polymers, when used for filtering aqueoussolutions, reject large molecules and particles without being blockedthereby. Small molecules such as water or small ions can penetratethrough such membranes. If there are no large molecules or particlespresent which could choke up pores, it is possible to use membranes orother forms of the new polymers with visible porosity or macroporosity.Besides of known methods for obtaining porous structure, it is possibleto obtain porous membranes also by casting polymer solutions withsolvents consisting at least partly of low volatile liquids such asdimethylformamide, and evaporate the solvent but incompletely. Suchmembrane is apparently almost dry, but when washed in water it becomesporous as the low volatile solvent is rapidly dissolved and the veryviscous solution coagulated. Instead of water the still partly wetmembrane can be washed in any other solvent capable of dissolving theremaining true solvent but incapable to dissolve the polymer. Byreacting such porous membranes with silver or cuprous ions one obtainslarge surface structures, very effective e.g. as catalysts or fordialysis of clear solutions.

Polymers and copolymers used as starting material containing strong acidgroups swell in water and aqueous solutions, and partly also in somepolar solvents like methanol, dimethylformamid etc. With large contentof strong acid groups the copolymers are water-soluble. Linearcopolymers having so high a content of nitrile groups that they are nomore water-soluble can be dissolved in aqueous solvent mixtures, e.g. ina dimethylformamidewater or dimethylsulfoxidewater mixture. The swellingcapacity of copolymers decreases with decreasing amount of strong acidgroups.

Silver and copper are in polymer complexes according to the inventioncomparatively strongly bound: E.g. silver cannot be removed with a 20%nitric acid. Silver is bound more firmly than copper: Silver complex isnot decomposed by 20% aqueous ammonia, while copper complex formstherewith the known dark blue complex solution. This depends, of course,also on the reactivity of the reagents with respect to each of the twometals.

By means of strong reducing agents the two metals are eliminated assuch, forming a dispersion in the polymer. They can then be dissolvede.g. in mineral acidsnitric for silver or hydrochloric for copper.Polymeric silver complexes react with halide ions, forming insolublesilver halides, finely dispersed in the swollen polymer. The grain sizeof the silver halides can be increased or decreased by maintaining thepolymer in swollen condition for an extended period of time, if desiredin presence of known peptizing agents, as known in the manufacture ofphotographic light-sensitive material. In order to increase the lightsensitivity, some gelatine solution can be added to the polymer solutionbefore casting and treating with silver and halide ions. Usualsensitizers can be added as well.

Copolymers of acrylonitrile or methacrylonitile with ethylene sulfonicor styrene sulfonic acid or with their soluble salts respectively are inmany respects similar to native gelatine, particularly if acrylamide ormethacrylamide is added as third monomer. The possibility of adjustingtheir properties by choosing suitable ratio between the monomers as wellas that of subsequent hardening by means of formaldehyde or similar, isvery desirable. Highly uniform light sensitive layers can be produced bycoating paper, glass, plastic films or foils with said copolymers,treating them with silver ions, removing excess thereof, and treatingthem again with halide ions. Preferably, after removing excessive halidesolution, the material is then treated again with silver ions, washed,and dried so that the light sensitive layer is composed from a silverhalide dispersed in the silver polymer complex.

Membranes can be manufactured not only by casting, as disclosed above,but also by extruding a viscous solution of a copolymer or polymermixture, having both nitrile and strong acid groups, into a coagulatingbath containing silver or cuprous ions. The same method is also suitablefor fibres. Membranes or fibres leaving the coagulating (spinning) bathare then thoroughly washed and stretched, in order to obtain planar orlinear molecular orientation.

Any of the methods mentioned above can be used also for manufacturingcompound or bipolar membranes, consisting of two inseparable layers, oneof them having prevailing amount of nitrile groups and the other anexcess of strong acid groups. .If such compound membranes are treatedwith silver or cuprous ions, they display different electrochemicalproperties on both sides.

The invention will be further illustrated by following non-limitingexamples.

EXAMPLE 1 Concentrated aqueous zinc chloride solution (d=l.95) wasgradually added to 2 mols of acrylonitrile and 1 mol of sodiumethylenesulfonate (the latter in the form of a 50% aqueous solution),until the two monomers were uniformly dissolved. A redox polymerizationcatalyst was then added in the form of 5 percent aqueous solutions ofpotassium pyrosulfite and ammonium persulfate (0.1% of each, on thetotal weight of the monomers). Finally, 0.0001% of coppersulfate-pentahydrate (in the form of an 0.1% aqueous solution) was addedas polymerization activator. The somewhat turbid solution was left topolymerize under carbon dioxide at room temperature. Next day theviscous copolymer solution thus obtained was poured in a thin stream inexcessive, vigorously stirred Water containing 0.2% of hydrochloricacid. The fibrous, highly swollen coagulate was then repeatedly washedin 0.5% nitric acid, and water. Excess of water was removed by filteringunder suction and the highly swollen copolymer was mixed, without beingdried, with threefold volume of dimethylformamide. After three hours ofstirring at 60 C. the almost clear solution was filtered. It containedabout of the copolymer. The still hot solution was degasified byapplying a vacuum and poured on an exactly horizontal polished plateglass in a 2 mm. thick layer. By slow evaporating the solvents a hard,clear membrane was obtained which could be easily removed from the glasswhen moistened with water. The membrane was repeatedly washed in 0.5nitric acid, in water, in a 1% aqueous solution of disodium salt ofethylenediamine tetra-acetic acid and again in water. Finally, the puremembrane was immersed into a 0.2 N silver nitrate solution. The membraneshrank thereby and became opaque and greyish white. After washing outthe excess of silver nitrate the membrane, having increased tenacity,could be used e.g. for filtering or dialysis. It could be easilycold-stretched, whereby its tenacity was further increased.

Silver could be removed from the membrane in an aqueous solution ofsodium thiosulfate. The membrane was then more swellable than prior tothe removal of silver, but considerably less swellable than the rawunoriented membrane. The difference of length caused by shrinking in 0.1N nitric acid and swelling in pure water, which was l50215% in the caseof the unoriented membrane, decreased to about after the reaction withsilver nitrate and to about 20-40% after the orientation and removal ofsilver.

EXAMPLE 2 Between two pieces of plates glass a sling of steel wire 0.8mm. was firmly held and three sides were immersed for a second into amelt of bee-wax and stearine (1:1). After a little while the wax mixturesolidified and a flat mold, opened on one side, was obtained, having 0.8mm. thickness. The mold was filled with a 10 C. cool monomer mixturethrough a flat funnel made from polyethylene foil. Monomer mixtureconsisted of 10 ml. of 50% aqueous solution of sodium ethylenesulfonate, 4 ml. of acrylonitrile, one drop of ethylene glycolbis-methacrylate and 8 ml. concentrated aqueous zinc chloride solution(d=1.98). Immediately prior to the casting the mixture was initiatedwith 5 drops of a 5% potassium pyrosulfite aqueous solution and withsame amount of ammonium persulfate. Gas bubbles were removed by pattingon the mold. The mold was then left standing at C. temperature. Gelpoint was reached in about minutes, after 3 hours the copolymerizationwas finished. The Wax layer on the border was cut and the mold carefullyopened under water. The copolymer foil thus obtained, first highlyplastified with zinc chloride soltuion, was then washed alternately in0.5 nitric acid, water, 5% ctiric acid and again in water. Last it wasimmersed into a 5% silver nitrate solution and then washed again. Themembrane thus obtained had similar properties like that in Example 1,except that it was less extensible and more elastic, due to the lowcross-linking caused by the small amount of glycol bis-methacrylateadded.

EXAMPLE 3 A 10% copper sulfate solution was reduced with hydroxylaminesulfate and powdery copper was added. A membrane prepared according toExample 2 was immersed into the solution thus obtained, containingcuprous ions. After 3 hours the membrane was washed in water.

It was substantially tougher and stronger than before, and the swellingcapacity was decreased similarly as when treated with silver ions. Themembrane had a weakly greenish color which did not disappear byprotracted washing in water.

EXAMPLE 4 Water-soluble copolymer of acrylonitrile, acrylamide andethylene sulfonic acid was prepared in following way: 57.5 g. of a 47%aqueous solution of sodium ethylene sulfonate, stabilized againstpolymerization by 0.2% sodiurn nitrite, was destabilized by adding 3 g.urea and acidified with concentrated hydrochloric acid to pH 2.Liberated gases were repeatedly sucked off. 7.1 g. acrylamide and 13.6ml. acrylonitrile were added and the whole was dissolved in 76 ml. ofoxygen-free water. 1 ml. of a 5% sodium pyrosulfite solution and thesame amount of ammonium persulfate was stirred in and the somewhatturbid solution was left standing under carbon dioxide at roomtemperature for 24 hours. The viscous solution thus obtained was pouredin two liters of anhydrous ethanol. The white coagulate wasreprecipitated by dissolving in Water again and precipitating inanhydrous ethanol, broken to small pieces and dried at 70 C.

A 20% solution of the copolymer in water was cast on a horizontal plateglass and the solvent slowly evaporated. The dry layer was treated with37% aqueous formaldehyde solution, acidified with 0.2% hydrochloricacid, for 2 hours at room temperature. The formaldehyde solution wasthen removed, the membrane washed with water, in which it becameinsoluble as a result of cross-linking with formaldehyde, and cut to twopieces. One was left in water as control, the other treated 5 minutes ina 5% silver nitrate solution and washed. The silver nitrate treatedmembrane shrank considerably, was opaque and its strength increased.

EXAMPLE 5 Free polyethylene sulfonic acid, obtained by treating neutralsodium polyethylene sulfonate solution in a column filled with astrongly acid cation exchanger, was mixed with an equivalent amount ofsilver nitrate. The solution was precipitated with a 5% solution ofpolyacrylonitrile in dimethylformamide. The precipitate-a polymeric saltof polyethylene sulfonic acid with a polyacrylonitrile-silver-complexpolycation is, in wet condition, a soft, greyish white plastic which canbe mechanically shaped and at least partly oriented. In dry conditionthe mass is hard and brittle; it can be ground to a powder which can bemixed with plastifiers and molded at increased temperatures.

Similar plastic is obtained when using monovalent copper ions instead ofsilver.

EXAMPLE 6 Dry powdered polyacrylonitrile was dissolved in a known mannerin concentrated cold nitric acid (65 weight percent) at 10-15 C. An 8%solution was obtained. Dry sodium salt of polyethylene sulfonic acid wasalso dissolved in concentrated nitric acid and to the 10% solution thusobtained the equivalent of silver nitrate in normal solution was added.When mixing the two clear solutions a white precipitate is formed whichpossesses, after having been thoroughly washed in water, similarproperties as the product obtained according to Example 5.

EXAMPLE 7 Membrane prepared according to Example 1 was immersed afterhaving been treated with silver nitrate solution and washed, into a 5%ammoniacal solution of hy drazine sulfate. It turned brownish black dueto precipitated metallic silver. During the subsequent washing withwater the membrane swelled considerably since the silver complex withnitrile groups was decomposed. By treating the membrane again in a 1%silver nitrate solution for 1 hour the membrane shrank again and lostits high swelling capacity. The membrane was suitable for filteringwater, wine and other beverage under simultaneous sterilization andartificial ageing. Without second treatment with silver nitrate thepolymer had very low oligodynamic activity since silver ions, liberatedby metallic silver, are readily caught by free nitrile and sulfonicgroups.

EXAMPLE 8 The copolymer solution prepared according to Example 1 inaqueous dimethylformamide was concentrated by evaporation to 11% drysubstance, filtered, degasified and spun through a spinneret with 0.2mm. holes into a spinning bath containing 5% of silver nitrate. Thefilaments were washed in hot distilled water and stretched. Then theywere cut to staple fibres. Metallic silver was liberated according toExample 7 and the washed fibres were treated with silver nitrate againand washed. They were very suitable for filtering and to other purposesmentioned in foregoing example.

EXAMPLE 9 The process according to Example 6 was repeated usingpolystyrene sulfonic acid instead of polyethylene sulfonic acid.Polystyrene sulfonic acid was obtained by careful sulfonation of linearpolystyrene with sulfuric acid, using silver sulfate as catalyst.Concentrated nitric acid must be carefully cooled when dissolvingpolystyrene sulfonic acid therein, in order to avoid excessivenitration. The greyish white precipitate had similar properties likethat gained in Example 6 or 5.

EXAMPLE 10 A 10% olyacrylonitrile solution (average molecular weight55,000) in cool concentrated nitric acid was mixed with a 10% solutionof sodium polyethylene sulfonate in the same solvent. The clear solutionwas extruded through a slit into a 10% aqueous silver nitrate solution.The polymer solution coagulated to a white opaque membrane which couldbe calendered in wet condition. It was suitable for filtering underpressure.

EXAMPLE 1 1 A flask with even edge was filled with a silver acetatesolution and tightly covered with a 0.5 mm. thick foil of regeneratedcellulose. Then it was turned down and immersed with the foil into asolution of a copolymer of acrylonitrile with sodium ethylene sulfonate(molar ratio 1.5:1) in aqueous dimethylformamide. Penetrating silverions coagulated the copolymer solution forming thus a porous membrane.The nature of the product could be changed by changing concentration ofthe silver nitrate solution, temperature, thickness and permeability ofthe foil and concentration of the copolymer solution.

EXAMPLE 12 The paper prepared according to Example 12 was, after havingbeen silvered and washed, treated with 0.1 N potassium bromide solution,containing also 1% of potassium chloride and 0.1% potassium iodide onthe total weight of halides. The paper was then kept for 1 hour at 30 C.in a sodium hydrocarbonate solution at pH 7.5-8. The washed and driedpaper had higher light sensitivity than that acc rdi g to E amp e 12.

EXAMPLE 14 The process according to Example 13 was repeated with theditference that a copolymer with increased swelling capacity (sulphurcontent 7%), containing 5 molar percent of acrylamide was used. 5%gelatin (on the weight of the copolymer) was added in the form of a warmaqueous solution prior to coating the paper. The paper was dried andhardened with gaseous formaldehyde, washed, treated with a 5% silvernitrate solution, washed again, treated with halide solution like inExample 13, washed in water, treated once again with a 5% silver nitratesolution, thoroughly washed and dried. It had still higher lightsensitivity than that prepared according to Example 13.

EXAMPLE 15 The raw membrane prepared according to Example 1, yetcontaining neither silver nor monovalent copper, was cut to small stripsand used for filling a small laboratory column, through which a verydiluted (about 0.003%) silver nitrate solutionwaste water from washingfibres according to Example 8was let through. By utilizing of thetheoretical capacity silver was quantitatively fixed. Theoreticalcapacity in this case means equivalent to that active groups (eithernitrile or sulfo), which are present in minor amount with respect to theother group.

EXAMPLE 16 A complex base, containing complex cations CN.Ag or --CN.Cu+,which cations are neutralized by anions of simple mineral acids such asN0 can be also prepared separately and then reacted with another polymerbearing strongly acidic groups such as SO Polyacrylonitrile (averagemolecular weight 55,000) was dissolved in concentrated nitric acid (65%HNO 15 C.) to a 10% solution. The solution was extruded through a 0.4mm. hole into a stirred 10% solution of silver nitrate in concentratednitric acid. The precipitate, containing complex cations --CN.Ag+ on thepolymeric chain and free anions N0 1 was washed in water to neutrality.It formed a greyish white plastic which was hot-calendered to a 0.5 mm.thick sheet. Onto this sheet, a solution of acrylonitrile-ethylenesulfonic acid copolymer, insoluble in water but soluble in aqueousdimethylformamide and dissolved therein, was poured in an uniformlythick layer and evaporated. The two layers were firmly bound by ioniccross-links between complex silver cations and sulfonic groups. Thebipolar membrane thus obtained could be used for building the oxygenside of a fuel cell. For this purpose, it is desirable to reduce silvercomplex cations first formed with an effective reducing agent such ashydrazine hydrate and then reconstitute the complex silver cations bytreating the polymer again with silver nitrate or silver acetatesolution as described in Example 7.

Free complex base can be obtained by washing the first prepared nitrate(see above) with diluted aqueous ammonia.

I claim:

1. A method for preparing a polymeric composition having bound thereto amonovalent metal cation of copper or silver comprising the steps ofcontacting a copolymer of an ethylenically unsaturated sulfonic acid orsalt thereof and a monomer selected from the group consisting ofacrylonitrile, methacrylonitrile, vinylidene cyanide and mixturesthereof with an aqueous solution of a salt of said metal for a period oftime sufficient to form a complex between the bound metal ions and saidpolymeric composition.

2. A method according to claim 1 further comprising adding a reducingagent to said complex, said reducing agent being capable of reducingsaid complexed metal cations to the elemental state and dispersing samein said composition, thereafter applying a solution of said metalcations to said composition to thereby reform sa d complex.

3. The method according to claim 1, wherein the number of monovalentcations is in excess of the available monomers.

4. The method according to claim 1, wherein said copolymerization isperformed under free radical polyrnerization in the presence of redoxinitiators containing less than 0.1% of metal bearing cations.

5. The method accordng to claim 1, wherein said composition is immersedin the solution so that said solution contacts each surface of saidcomposition.

6. The method according to claim 1, including the step of applying tosaid complex compound a reducing agent until said bound metal ions arereduced to the elementary state and dispersed in the polymericcomposition and then after applying to said composition having theelementary metal dispersed therein, said solution of ions of monovalentsilver or copper until said complex compound is again formed.

7. The method according to claim 2, wherein said metal cations aresilver ions, and said complex compound is 20 contacted with halide ionsuntil a portion of the bound 10 metal cations is converted to silverhalide insoluble in water dispersed in the surface of said composition.

8. The method according to claim 7, wherein said surface having saidsilver halide dispersed therein is contacted with ions of monovalentsilver or copper until said complex is reformed.

References Cited UNITED STATES PATENTS 3,056,169 10/ 1962 Hendricks 18573,296,234 l/1967 Ehrig 26088.7

3,322,734 5/1967 Rees 26079.3

3,328,333 6/ 1967 Dannelly 260-304 JOSEPH L. SCHOFER, Primary ExaminerC. A. HENDERSON, JR., Assistant Examiner US. Cl. X.R.

